Cooling arrangement and method for cooling an at least two-stage compressed air generator

ABSTRACT

The invention relates to a cooling arrangement for an at least two-stage compressed air generator ( 01 ). The cooling arrangement comprises an intercooler ( 04 ), which is arranged between a first and a second compressor stage ( 02, 03 ), an aftercooler ( 05 ), which is arranged after the second compressor stage ( 03 ), and a subassembly cooler ( 08 ), which absorbs heat from further subassemblies of the compressed air generator ( 01 ). A coolant circuit comprises a main cooler ( 07 ), the cold side of which supplies a cooled coolant having a low temperature parallel to the respective coolant inlet of the intercooler ( 04 ), of the aftercooler ( 05 ) and of the subassembly cooler ( 08 ), and the hot side of which receives the heated coolant having a high temperature exiting in parallel at the respective coolant outlet of the intercooler ( 04 ) and of the aftercooler ( 05 ). The coolant outlet of the subassembly cooler ( 08 ) is connected to a feed inlet ( 12 ) of the intercooler ( 04 ) and/or of the aftercooler ( 05 ). The feed inlet ( 12 ) is arranged between the coolant inlet and the coolant outlet, at a point at which the intermediate temperature of the coolant in the intercooler ( 04 ) or in the aftercooler ( 05 ) corresponds to the exit temperature of the coolant at the subassembly cooler ( 08 ) ±20%. 
     The invention furthermore relates to a method for cooling an at least two-stage compressed air generator.

The invention relates to a cooling arrangement for an at least two-stage compressed air generator. Such a compressed air generator, also called a compressor, comprises a liquid-cooled intercooler, which is arranged between a first and a second compressor stage, in order to cool the precompressed air discharged from the first compressor stage before it enters the second compressor stage, and a liquid-cooled aftercooler, which is arranged after the second compressor stage, in order to cool the air compressed by it. Furthermore, a liquid-cooled subassembly cooler is provided, which absorbs heat from further subassemblies of the compressed air generator, in order to cool power electronics or drives and gears of the compressor stages, for example. A coolant circuit runs via a main cooler, the cold side of which supplies a coolant to the respective coolant inlet of the intercooler, of the aftercooler and of the subassembly cooler, and the hot side of which receives the heated coolant exiting at the coolant outlet of the intercooler and of the aftercooler.

The invention furthermore relates to a method for cooling an at least two-stage compressed air generator.

A wide variety of designs of compressors are known for the compression of gaseous media, in particular for the generation of compressed air. For example, DE 601 17 821 T2 shows a multi-stage screw compressor with two or more compressor stages, each compressor stage comprising a pair of rotors for compressing a gas. Further provided are two or more variable-speed drive means, each drive means driving a respective compressor stage.

EP 2 886 862 A1 describes a compressor having a motor, a drive shaft, a crank mechanism connected to said driveshaft, at least one compressed air generating device, a crankcase and a compressed air storage tank. All the components are cooled by means of a cooling air flow generated by a fan wheel.

DE 10 2017 107 602 B3 discloses a compressor plant having a plant housing in which a plurality of heat-generating plant components are arranged. These include a twin-screw compressor having two compressor stages, which serve to compress a gaseous medium, in particular to generate compressed air. The plant housing furthermore contains an air-water cooler, a fan, which generates a cooling air flow, and air guide elements which guide the air heated by the plant components to the air-water cooler.

EP 2 529 116 B1 describes a method for recovering energy during the compression of a gas by a compressor with two or more pressure stages. Downstream of the compressor, a heat exchanger having a primary and a secondary part is provided. The gas compressed from one pressure stage is guided through the primary part; a coolant is guided through the secondary part.

WO 2015/172206 A9 shows a compressor with at least two compression stages in series and at least two coolers, specifically an intercooler between the compression stages and an aftercooler downstream after the last compression stage. At least two of the coolers are configured as split coolers, such that the secondary side through which the coolant flows is divided into two stages, in order to cool the gas flowing through on the primary side in a hot and a cool stage. The two stages of the secondary side are connected together in different cooling circuits. For example, each of the first stages of the plurality of coolers and each of the second stages are connected in series.

DE 31 34 844 A1 describes a method for optimising the energy efficiency of a compression process, in particular for multi-stage compression with centrifugal and piston compressors. For this purpose, a heat pump is integrated into a compressor plant. Preferably, at least one evaporator of the heat pump is incorporated into the pipelines of the cooling stages which carry the heated cooling water.

US 2018/0258952 A1 describes a compressor module, which comprises a compressor having a housing with an integrated compressor cooler. According to one embodiment, two such modules can be combined with one another, such that a low-pressure compressor module and a high-pressure compressor module are connected in series. Each of the two compressor modules has a liquid-cooled cooler, which cools the compressed air at the outlet of the module. Furthermore, a motor cooler and a structural-element cooler are provided, the coolant circuits of which are connected to those of the compressor cooler.

In general, compressor plants of this type always require the dissipation of more or less large amounts of heat, in order to avoid overheating of individual components or of the entire plant. Up to now, the entire plant has been regularly cooled by cooling air, with heated exhaust air usually being discharged unused into the environment. The heat is then either lost or can only be recovered inefficiently from the exhaust air. Some plants additionally contain a heat exchanger, the secondary heat transport medium of which absorbs heat from a primary cooling circuit of the compressor and transports it away. The dissipated heat can then be used by an external consumer.

One object of the present invention, on the basis of the prior art, consists, on the one hand, in ensuring efficient cooling of such compressed air generators (compressor plants), while reducing the equipment-related outlay, and on the other hand, however, also in permitting more efficient recovery of heat with respect to the entire compressed air generator.

This object is accomplished by a cooling arrangement for an at least two-stage compressed air generator according to appended Claim 1. Preferred embodiments of the cooling arrangement are specified in dependent Claims 2 to 7. Furthermore, the object is accomplished by a method for cooling an at least two-stage compressed air generator according to appended Claim 8. Advantageous versions of the method are specified in dependent Claims 9 and 10.

The cooling arrangement according to the invention is suitable for cooling a compressed air generator, preferably in the manner of a compressor plant, with at least two compressor stages. The cooling arrangement comprises at least one liquid-cooled intercooler, which is arranged between a first and a second compressor stage, in order to cool the precompressed air discharged from the first compressor stage before it enters the second compressor stage. A liquid-cooled aftercooler is arranged after the second, or last, compressor stage, in order to cool the further compressed air. In the simplest case, the generated compressed air is provided to external units after flowing through the aftercooler. In variations, the compressed air generator can also have more than two compressor stages and correspondingly additional intercoolers.

Furthermore, the cooling arrangement comprises a liquid-cooled subassembly cooler, which absorbs heat from further subassemblies of the compressed air generator and discharges it to the coolant. Like the other coolers, the subassembly cooler is arranged in the housing of the compressed air generator and is formed, for example, as a finned cooler, cooling plate, heat pipe or the like. The subassembly cooler can be composed of a plurality of individual coolers and serves to dissipate heat in particular from the drives of the compressor stages and the power electronics that are required for controlling the compressed air generator.

The cooling arrangement has a coolant circuit, which comprises a main cooler in order to dissipate the heat, which is absorbed by the coolant in the other coolers, out of the compressed air generator. The cold side of the main cooler delivers cooled coolant at a low temperature directly to the respective coolant inlet of the intercooler, of the aftercooler and of the subassembly cooler. The coolant inlets of the intercooler(s), aftercooler and subassembly cooler(s) are connected in parallel, such that the coolant is fed to them at the same low temperature. The hot side of the main cooler receives the heated coolant directly from the respective coolant outlet of the intercooler (or the plurality of intercoolers) and of the aftercooler, or indirectly from these if a heat exchanger is interposed for heat recovery, as described further below. The coolant outlets of the intercooler(s) and the aftercooler are connected in parallel and deliver the heated coolant at a high temperature to the main cooler, where appropriate via the heat exchanger.

It is essential to the invention that the coolant outlet of the subassembly cooler is not connected parallel to the coolant outlet of the intercooler or aftercooler. This prevents the coolant from being cooled from the high temperature at the outlet of the intercooler and aftercooler by the admixture from the subassembly cooler, since the subassembly cooler regularly delivers lower temperatures of coolant, owing to the smaller amount of heat to be dissipated. Instead, the coolant of the subassembly cooler is fed to a feed inlet of the intercooler and/or the aftercooler, the feed inlet being arranged between the coolant inlet and the coolant outlet, at a position at which the intermediate temperature of the coolant in the intercooler or aftercooler corresponds to the exit temperature of the coolant at the subassembly cooler ±20%. Preferably, the temperature of the coolant admixed from the subassembly cooler deviates by less than t10%, in particular by less than ±3%, from the temperature at the point of admixture in the intercooler or aftercooler.

The same cooling medium (preferably water) is thus used for the intercooler, the aftercooler and the subassembly cooler. Thus, not only heat from the compressed air but also the heat from subassemblies, e.g. electric motors, converters, compressor stages, gear units etc. can be accumulated in the coolant and transported away from it. The majority of the waste heat from the entire compressed air generator is thus also available for heat recovery.

A further advantage of the invention is that the main cooler can be designed to be significantly smaller, which leads to a considerable reduction in the size of the coolant circuit and thus in the overall costs of the compressed air generator. Owing to the described targeted feeding of the coolant delivered from the subassembly cooler at the intermediate temperature into the intercooler and/or aftercooler, the high temperature at the outlet of the intercooler and the aftercooler can be kept at a high level, preferably in the region of 90° C. This leads to a large temperature difference at the main cooler, such that its cooling area can be kept smaller than if the inlet temperature at the main cooler were lower. The required cooling area is proportional to the temperature difference between the inlet temperature (high temperature) and the desired outlet temperature (low temperature).

According to an advantageous embodiment, the coolant delivered from the subassembly cooler is fed both to the intercooler and to the aftercooler via the respective feed inlet.

According to a particularly preferred embodiment of the cooling arrangement, a heat exchanger is interposed in the coolant circuit between the respective coolant outlet of the intercooler and of the aftercooler and the coolant inlet of the main cooler. The heat exchanger thus has all the heat that is fed to the coolant available for transfer to a heat carrier medium.

Preferably, the main cooler is a water-air cooler or a water-water cooler or a combination cooler, which uses water and air optionally as a cooling medium. The user of the compressed air generator is therefore free to decide whether to implement the main cooling with the aid of fan-assisted exhaust air cooling or by connecting to an external liquid cooling medium.

It is advantageous if the intercooler and/or the aftercooler have a plurality of feed inlets, to which the coolant optionally can be fed from the coolant outlet of the subassembly cooler. In particular, a distributor unit is arranged between the coolant outlet of the subassembly cooler and the feed inlets, which distributor unit supplies, in a temperature-controlled manner, that feed inlet at which the intermediate temperature of the coolant in the intercooler or aftercooler is closest to the exit temperature of the coolant at the subassembly cooler.

The intercooler, the aftercooler, the subassembly cooler, the heat exchanger, the first and second compressor stages and an electronic control unit are conveniently arranged within a common device housing. The cooling arrangement is thus an integral constituent of the compressed air generator, such that the installation outlay for the user is kept to a minimum.

The method according to the invention for cooling an at least two-stage compressed air generator comprises the following steps:

-   -   guiding a cooling medium in a coolant circuit through a main         cooler and through a first liquid-cooled intercooler connected         in series with the main cooler, which intercooler thus cools air         precompressed by a first compressor stage;     -   guiding the cooling medium in the coolant circuit through an         aftercooler that is likewise connected in series with the main         cooler and connected parallel to the intercooler, which         aftercooler thus cools air post-compressed by a second         compressor stage;     -   feeding the cooling medium cooled in the main cooler to a         liquid-cooled subassembly cooler, which absorbs heat from         further subassemblies of the compressed air generator;     -   feeding the heated cooling medium, which is discharged from the         subassembly cooler, via a feed inlet into the intercooler and/or         into the aftercooler, the feed taking place at a position in the         intercooler or in the aftercooler at which the intermediate         temperature of the coolant in the intercooler or aftercooler         corresponds to the exit temperature of the coolant at the         subassembly cooler ±20%, preferably these two temperatures are         substantially the same.

Further advantages and details of the invention emerge from the following description of a preferred embodiment with reference to the drawings. In the drawings:

FIG. 1 shows a block diagram of a cooling arrangement according to the invention with deactivated heat recovery;

FIG. 2 shows a block diagram of the cooling arrangement with activated heat recovery.

FIG. 1 shows the simplified block diagram of a compressed air generator 01 or a compressor plant. The block diagram mainly comprises the essential elements of a cooling arrangement and omits other units of the compressed air generator. The compressed air generator comprises at least a first compressor stage 02 and a second compressor stage 03. The air precompressed in the first compressor stage 01 is supplied at a temperature of, for example, 200° C. to an intercooler 04 for cooling and exits said intercooler 04 at approximately 50° C., in order to then be further compressed by the second compressor stage 03. The finally compressed air exits the second compressor stage 03 at a temperature of approximately 200° C. and is then fed to an aftercooler 05 for renewed cooling, so that the compressed air is finally delivered to external units at approximately 50° C. For the dissipation of heat, a main cooler 07 delivers a cooling medium, preferably cooling water, to its cold side at a temperature of 45° C., for example. The cooling water A is delivered at this low temperature parallel to the inflow of the intercooler 04, the aftercooler 05 and a subassembly cooler 08. The cooling water flows through the intercooler 04 and the aftercooler 05 to absorb the heat of the compressed air and is delivered back to the hot side of the main cooler 07 at a high temperature of 90° C. for example. Prior to this, in the depicted design, the cooling water flows through one more heat exchanger 09, which, however, is deactivated in FIG. 1, so that the cooling water temperature at the inlet and outlet of the heat exchanger 09 is virtually unchanged. The heat is discharged at the main cooler 07, in order to bring the cooling water back to a low temperature. The cooling is assisted, for example, by a fan 11, which discharges a heated exhaust air at a temperature of 40° C., for example.

A special feature of the cooling arrangement is that, after flowing through the subassembly cooler 08, the cooling water is not guided directly to the main cooler 07 or to the upstream heat exchanger 09 parallel to the cooling water of the intercooler and the aftercooler. Instead, the cooling water outlet of the subassembly cooler is connected in each case to a feed inlet 12 at the intercooler 04 and at the aftercooler 05. The feed inlet 12 can alternatively also be provided only at one of the two coolers 04, 05 and its position is selected such that an intermediate temperature of 57° C., for example, prevails there in the cooler 04, 05. The intermediate temperature is to correspond substantially to the outlet temperature of the cooling water B, which is delivered from the subassembly cooler 08. The cooling water B is thus admixed again with the cooling water A in the intercooler 04 and/or in the aftercooler 05 and further heated there to the high temperature.

FIG. 2 shows the simplified block diagram of the compressed air generator 01 or the compressor plant in a modified operating state, specifically with activated heat recovery at the heat exchanger 09. This results in a drop in the temperature of the heated cooling water from 90° C. to 50° C., for example, at the heat exchanger 09. The extracted heat is available for other applications, such as for heating purposes, for example.

LIST OF REFERENCE NUMBERS

-   01 compressed air generator/compressor plant -   02 first compressor stage -   03 second compressor stage -   04 intercooler -   05 aftercooler -   06 - -   07 main cooler -   08 subassembly cooler -   09 heat exchanger -   10 - -   11 fan -   12 feed inlet 

1. A cooling arrangement for an at least two-stage compressed air generator (01), comprising a liquid-cooled intercooler (04), which is arranged between a first and a second compressor stage (02, 03), in order to cool the precompressed air discharged from the first compressor stage (02) before it enters the second compressor stage (03); a liquid-cooled aftercooler (05), which is arranged after the second compressor stage (03), in order to cool the air compressed by said second compressor stage (03); a liquid-cooled subassembly cooler (08), which absorbs heat from further subassemblies of the compressed air generator (01); a coolant circuit, which has a main cooler (07), the cold side of which feeds a cooled coolant having a low temperature to the respective coolant inlet of the intercooler (04), of the aftercooler (05) and of the subassembly cooler (08) in parallel, and the hot side of which receives the heated coolant having a high temperature which exits in parallel at the respective coolant outlet of the intercooler (04) and of the aftercooler (05); characterised in that the coolant outlet of the subassembly cooler (08) is connected to a feed inlet (12) of the intercooler (04) and/or the aftercooler (05), wherein the feed inlet (12) is arranged between the coolant inlet and the coolant outlet, at a point at which the intermediate temperature of the coolant in the intercooler (04) or in the aftercooler (05) corresponds to the exit temperature of the coolant at the subassembly cooler (08) ±20%.
 2. The cooling arrangement according to claim 1, characterised in that a heat exchanger (09) is interposed in the coolant circuit between the respective coolant outlet of the intercooler (04) and of the aftercooler (05) and the hot side of the main cooler (07).
 3. The cooling arrangement according to claim 1 or 2, characterised in that the main cooler (07) is a water-air cooler or a water-water cooler or a combination cooler, which uses water and air optionally as a cooling medium.
 4. The cooling arrangement according to claim 3, characterised in that the main cooler (07) comprises a fan (11).
 5. The cooling arrangement according to any one of claims 1 to 4, characterised in that the intercooler (04) and/or the aftercooler (05) have a plurality of feed inlets (12), to which the coolant can be optionally fed from the coolant outlet of the subassembly cooler (08).
 6. The cooling arrangement according to claim 5, characterised in that a distributor unit is arranged between the coolant outlet of the subassembly cooler (08) and the feed inlets (12), which distributor unit supplies, in a temperature-controlled manner, that feed inlet (12) at which the intermediate temperature of the coolant in the intercooler (04) or aftercooler (05) is closest to the exit temperature of the coolant at the subassembly cooler (08).
 7. The cooling arrangement according to any one of claims 1 to 6, characterised in that at least the intercooler (04), the aftercooler (05), the subassembly cooler (08), the heat exchanger (09), the first and second compressor stages (02, 03) and an electronic control unit are arranged within a common device housing.
 8. A method for cooling an at least two-stage compressed air generator (01), comprising the following steps: guiding a cooling medium in a coolant circuit through a main cooler (07) and through a first liquid-cooled intercooler (04) connected in series with the main cooler (07), which intercooler (04) thus cools air precompressed by a first compressor stage (02); guiding the cooling medium in the coolant circuit through an aftercooler (05) likewise connected in series with the main cooler (07) and connected parallel to the intercooler (04), which aftercooler (05) thus cools air post-compressed by a second compressor stage (03); feeding the cooling medium cooled in the main cooler (07) to a liquid-cooled subassembly cooler (08), which absorbs heat from further subassemblies of the compressed air generator (01); characterised in that the heated cooling medium exiting the subassembly cooler (08) is fed via a feed inlet (12) into the intercooler (04) and/or into the aftercooler (05), wherein the feed takes place at a position (12) in the intercooler (04) or in the aftercooler (05) at which the intermediate temperature of the coolant in the intercooler (04) or aftercooler (05) corresponds to the exit temperature of the coolant at the subassembly cooler (08) ±20%.
 9. The method according to claim 8, characterised in that the cooling medium heated in the intercooler (04) and in the aftercooler (05) is fed to a heat exchanger (09) for heat recovery before it is returned to the main cooler (07).
 10. The method according to claim 8 or 9, characterised in that the heated cooling medium exiting the subassembly cooler (08) is fed via one of a plurality of feed inlets (12) into the intercooler (04) and/or into the aftercooler (05), wherein the feed inlet (12) is selected in such a way that the intermediate temperature of the coolant in the intercooler (04) or aftercooler (05) at said feed inlet (12) corresponds to the exit temperature of the coolant at the subassembly cooler (08). 